The present invention relates to a vertical resistive combustion furnace for use in the combustion of a sample in a stream of oxygen to convert the sample into oxides of its constituent components which are then analyzed. In the case of hydrogen, for example, the hydrogen is converted to water which is analyzed.
In the past, it has been common practice to have combustion furnaces for use in the analysis of solid and liquid materials arranged with the combustion tube mounted horizontally. The input to the combustion tube was open and shielded by a stream of oxygen while the distal end of the combustion tube was closed. Many combustion tubes look like large horizontally disposed test tubes having a rounded end. An eduction tube was either inserted into the tube or provided along the outer surface of the tube and connected by a suitable glass or ceramic fitting to the combustion tube near the closed end. A sample to be analyzed was placed into a boat which was shoved into the horizontal tube. The rod used to move the sample was marked so that the laboratory technician could determine where the sample was relative to the combustion zone of the furnace. The sample could not be seen since the furnace was heavily insulated. Horizontal combustion furnaces have two significant drawbacks: 1) the sample has to be pushed in a suitable carrier to the hot zone of the furnace, and 2) the combustion tube is open to the atmosphere so the combustion products have to be pumped or drawn from the combustion tube.
In an attempt to overcome the problems associated with horizontal combustion tubes, the assignee of the present patent application launched a research effort to develop a vertical combustion furnace. This research effort resulted in the development of such a furnace which is the subject of U.S. patent application Ser. No. 659,707 entitled ANALYTICAL FURNACE which is incorporated herein by reference. The vertical combustion furnace disclosed in the aforementioned patent application is a significant improvement over horizontal combustion furnaces.
The combustion furnace employs a pair of coaxial tubes, the bottoms of which are supported and spaced by a machined stainless steel base. In assembling the furnace, the stainless steel base must be fit into the bottom of the furnace and then the outside combustion tube inserted, followed by the inside combustion tube which contains packing to support the combustion crucible in the center of the combustion zone of the furnace. The vertical furnace enables samples to be dropped through a lance into the crucible rather than being pushed. In view of the height of the base, the length of the combustion zone in the furnace is shortened. Also, the combustion products are removed through a port in the supporting base at the bottom of the furnace. While the furnace functions well, the overall construction of the furnace is relatively complex. For example, the inner combustion tube contains packing and reagent materials used to complete the combustion of the sample. These materials are put in place in the inner combustion tube after the tube is in place in the combustion furnace. Also, since an open ended tube was used to contain the packing material, it was difficult to replace the packing material in the event it became clogged.
U.S. Pat. No. 4,622,009 issued Nov. 11 1986, and assigned to the assignee of the present application discloses a vertical combustion furnace employing a U-shaped combustion tube. The sample to be combusted can be dropped into a crucible supported in one side of the tube while the reagent materials used to assure complete oxidation of the constituent elements are contained in the other leg of the U-shaped tube. While this furnace functioned for its intended purpose, it was relatively complex.